Recently, with increasing development of information industries, portable information devices such as notebook computers or personal digital assistants are widely used in many instances. In a case that a portable information device is used in a dim environment, the numbers and characters marked on the keys of the keyboard of the portable information device are not clearly visible. In other words, the dim environment becomes hindrance from operating the keyboard. In addition, if the keyboard is used in the dim environment, the user is readily suffered from vision impairment. For solving these drawbacks, a luminous keyboard has been disclosed. The luminous keyboard could be used in the dim environment in order to enhance the applications thereof. Moreover, by changing the arrangement of luminous regions, the information device having the luminous keyboard is more aesthetically-pleasing and thus the competiveness thereof is enhanced.
FIG. 1 is a schematic cross-sectional view illustrating a luminous keyboard according to the prior art. As shown in FIG. 1, the luminous keyboard 1 comprises a reflector 11, a light guide plate 12, a metallic base pate 13, a membrane circuit board 14, a plurality of keys 15 and light-emitting elements 16. The membrane circuit board 14 comprises a lower wiring board 141, an upper wiring board 142 and an intermediate board 143. The intermediate board 143 is arranged between the lower wiring board 141 and the upper wiring board 142. The lower wiring board 141, the intermediate board 143 and the upper wiring board 142 are made of transparent light-guiding material. The transparent light-guiding material includes for example polycarbonate (PC) or polyethylene (PE).
Please refer to FIG. 2, which is a schematic exploded view illustrating a membrane circuit board of the luminous keyboard of FIG. 1. The upper wiring board 142 has a first circuit pattern 1421. The first circuit pattern 1421 comprises a plurality of silver paste conductor lines 14211 and a plurality of upper contacts 14212. The lower wiring board 141 has a second circuit pattern 1411. The second circuit pattern 1411 comprises a plurality of silver paste conductor lines 14111 and a plurality of lower contacts 14112. The intermediate board 143 has a plurality of perforations 1431 corresponding to the upper contacts 14212 and the lower contacts 14112. Each of the upper contacts 14212 and the corresponding lower contact 14112 are collectively defined as a membrane switch 144. In addition, each key 15 has a keycap 151 and an elastic element 152. The elastic element 152 is arranged between the keycap 151 and the membrane circuit board 14.
When any key 15 is pressed down by a user, the elastic element 152 is compressed by the keycap 151, so that the corresponding upper contact 14212 is pushed by the elastic element 152. Consequently, the upper contact 14212 is contacted with the corresponding lower contact 14112 through a corresponding perforation 1431. In such way, the corresponding membrane switch 144 is electrically conducted, and the luminous keyboard 1 generates a corresponding key signal. Whereas, when the depressing force exerted on the keycap 151 is eliminated, an elastic force provided by the elastic element 152 is acted on the keycap 151. Due to the elastic force, the keycap 151 is moved upwardly and returned to its original position.
The light-emitting elements 16 are arranged at bilateral sides of the light guide plate 12 for emitting light beams. The light beams are incident to the light guide plate 12. The light guide plate 12 is disposed on the reflector 11. The metallic base plate 13 has a plurality of opening 131. The openings 131 are aligned with respective keys 15. After the light beams are incident to the light guide plate 12, the light beams are diffused into the whole light guide plate 12. Then, portions of the light beams are upwardly directed from the light guide plate 12 to the membrane circuit board 14 and the keys 15 through the perforations 131. In addition, other portions of the light beams are directed downwardly from the light guide plate 12 to the reflector 11 and reflected by the reflector 11, so that the reflected light beams are also directed upwardly. In such way, the light beams provided by the light-emitting elements 16 can be well utilized to illuminate the keys 15. However, the membrane circuit board 14 of the conventional luminous keyboard still has some drawbacks.
FIG. 3 schematically illustrates a light path in the lower wiring board of the membrane circuit board of FIG. 2. As shown in FIG. 3, the second circuit pattern 1411 is disposed on the top surface of the lower wiring board 141, and the second circuit pattern 1411 comprises a plurality of silver paste conductor lines 14111. Since these silver paste conductor lines 14111 have functions of collecting and scattering the light beams, after the light beams L1 provided by the light-emitting elements 16 are introduced into the lower wiring board 141 through the openings 141 of the metallic base plate 13, the light beams L2 passing through the silver paste conductor lines 14111 of the second circuit pattern 1411 seem very bright. Since most of the silver paste conductor lines 14111 are not aligned with the keys, the amount of light beams to be directed to the keys 15 to illuminate the keys 15 are consumed by the silver paste conductor lines 14111. That is, although the light beams L1 are mostly directed to the keys 15 according to the original design, the silver paste conductor lines 14111 may consume the amount of the light beams L2 because of the characteristics thereof. Consequently, only the light beams L3 are retained to be utilized by the luminous keyboard 1. Under this circumstance, the keys 15 of the luminous keyboard 1 fail to be effectively illuminated.
Therefore, the light use efficiency of the membrane circuit board 14 of the luminous keyboard 1 is insufficient and needs to be further improved.